My first 50 was canon 1.4 which was okay. I, however, wanted a better build and optical quality. It is important for me lenses "feel" right because i am tactile person (lack of AF is not a concern). I then bought the sigma's 50 1.4 and while i thought that lenses handled better than the canon it still lacked that solid build quality i dreamed of. So, i bought zeiss 50 f2 makro-planar. It is a remarkable lens: the build quality is more solid than nikon's old manuals but that is not necessarily a deciding point (i prefer the rubberised focusing ring on the nikkor than a metal and unpleasant to use ring on the zeiss).
While the zeiss is a great lens there were a few problems with it (sorry if i'm way off the topic here but i'll get back to 50 1.2 soon): first, it is much chunkier than the nikkor (physically larger and heavier); second, it is much more expensive (at least twice the price when both lenses are bought new) so while the performance of the zeiss is great the price/performance ratio is high -> go to photozone for more info); third, the zeiss has a very long focusing throw (around 270 degrees) which cost me a few shots when i had to quickly change the focusing distance. fourth, the macro capability on the zeiss which really is just a close-up feature proved to be rather useless for my type of photography (should have known better): it is handy for taking pictures of flowers or static objects but without the AF and IS it gets quite challenging. please don't get me wrong, the zeiss is a great lens both mechanically and optically and i really liked it until i bought the nikkor 50 1.2.

The thing i really missed with the zeiss was an extra stop of light (down to 1.4 plus 1/3 with 1.2). That really opened up a lot of possibilities for my type of photography. I use the 50 1.2 on my canon 7D and i like the combo. A native nikon body would be much better (particularly on a full frame like the d700) because of some metering issues with canons: at times inconsistent metering and you'll have to stop down the lens to meter properly. Many say the lens is very soft wide open but again if you can focus spot on you will be rewarded with some reasonably sharp images. If you use a cropped sensor body make sure you have a good quality focusing screen: i use katzeye split prism focusing screen with optibrite treatment and focusing now is so much easier than before. If you're really concerned about sharpness and very high contrast you'd be happy to know that the lens performs very well when stopped down just to f2. I did some basic tests and i noticed that the nikkor @f2 was a bit sharper and more contrasty than the zeiss wide open. So, if you don't need the close up feature save yourself some money and go for the nikkor: these gems are still available for purchase new. The lens, however, is really meant to be shot wide open and that's what i do 90% of the time: the images come out reasonably sharp with a dreamy effect. Also bear in mind the fact sharpness is far not everything (at least not with portraits). Want some really sharp images go for a macro lens. The zeiss was so sharp at f4 the portrait shots looked unbelievably ugly.

The nikkor is very light and compact, has a small front element (no need for large filters) and is built exceptionally well. The focusing ring is not too tight nor too loose and feels comfortable in hands due to its rubberised coating. The aperture ring is easy to operate and clicks in solidly. The bokeh has some character: it may sometimes distracting especially in the highlights but you can always use it as an advantage and make your images look more artistic. In fact, some photos i've seen have bokeh as the main subject of the photo so don't get discouraged and just shoot more until you hit the spot.

Overall, a truly great lens. It is actually quite versatile too: f1.2 lets in a lot of light for night shooting and stopping down to f2 and beyond adds more contrast and sharpness for the type of photography that requires those.

Magnificent Lens! Of course the lack of AF will not allow you to shoot moving objects with open aperture since the DOF is extremely small at f1.2 but for artistic still shots this is a superb lens.

A lot of reviewers say this lens is soft at f1.2. This is so NOT true. It is in fact tack sharp but the depth of field is so shallow, that it is very difficult to have the focus exactly where it should be. Everyone telling you this lens is soft at the open end is just unable to cope with the unforgiving combination of very shallow depth of field and manual focussing.

Incredibly beautiful bokeh. I own the 1978-1980 model which only has 7 aperture blades (all newer models have 8 blades) and is said to have a not so beautiful bokeh. But i still love the bokeh of mine.

Strengths: Not a neutral antiseptic lens, it has a strong character, a "look".
The build on the AIS in second to none, feels like a piece of panavision glass.
Cinematic, beautiful DOP.
Fast Fast Fast!

Weaknesses: Hard to find exact focus wide open.
Some may not like the character of the bokeh.

Bottom Line:

This is a lovely lens that needs to be judged for is character rather than the more antiseptic specs that usually dominate lens reviews. It has a level of artfulness that all other of my lenses lack. Painterly and cinematic would be perfect adjectives. Sure it has some CA, the bokeh is not buttery smooth, it is hard to find exact focus due to such a shallow DOP (6mm). Because of this, a lot of reviewers say it's soft. Good rule is to shoot a series. With the shallow DOP, click off 5 or 6 shots, your body moves enough to bring objects in and out of focus.

Don't force this lens to be like your other lenses, let it make you do what it wants.

Something about this lens makes everything special, like I have never experienced, not even with my 85mm 1.4. I shot the inside of a closed diner with nothing more than ambient street light and it was amazing. The color of the sky after dusk was more vibrant than I have ever experienced. And I shot all this at 200 or 400 ISO wide open with a 60th shutter. Every time I would look at the back of my D700 I was giddy.

Strengths: Exceptional aperture of f1.2 is killer for ambient light and low-light applications. Candle-lit portraits are dreamy wide open on this baby. As you would expect, the shallow depth of field at f1.2 is wonderful (if you're into shallow, of course), as is the bocce. Contrast is quite low on the lens, and images can often have a milky quality that is quite impressionistic and painterly. I must say that for sharper, contrastier images I favour my f1.4 Nikon AIS lens, and tend to use this more as an 'effect' lens.

Weaknesses: It's bulky as you'd expect, with large front and rear elements. Not the sharpest Nion lens I've looked through.

Bottom Line:

I tend to only use this lens in extreme low light conditions, taking advantage of it's exceptionally fast f1.2 aperture. Good for dreamy shallow DOF portraits and shooting in ambient light after dark.

Similar Products Used: Nikon f1.4 AIS lens...tends to produced higher contrast and sharper images at wider aperture settings. I tend to favour the f1.4 for general use. I have a wide range of manual focus Nikon lenses and swear by them!

Weaknesses: Manual focus and unforgiving. You need a camera with a good viewfinder... would highly recommend you have a split screen in your view finder for best results.

Bottom Line:

The lens is very fast. If you want a shallow depth of field this is the best lens you can find. I read a mixed bag of reviews here and the people seem to either love it or hate it. The ones that hate it all complain that it is soft - clearly they don't know how to focus properly. This lens is very sharp when in focus when out of focus by just a small amount it will give you blur that can ruin the shot.... in other words the lens is very unforgiving.

You need to realize that it is only manual focus and as such if you have a cheaper camera with a poor viewfinder this lens is likely to give you soft results because you wont be able to get a good focus. When I used it on an older digital camera with a less than perfect viewfinder I take shots while slowly moving the focus ring because I know I can't focus it perfectly with the viewfinder. On a good camera it is priceless.